| There are higher and higher requirements for the DC/DC converters due to the development of the distributed power supply system. The developing trend of the DC/DC converters is high efficiency, high power density, low voltage, high current, fast dynamic response and high reliability. As the restriction of the isolated feedback loop, the traditional primary-side control converters can not meet the requirements on fast dynamic response, high reliability and so on. The secondary-side control technology, in which the controller is placed at the secondary side of the converter, can reduce the closed-loop delay mostly and eliminate such non-reliable devices as optocoupler, so as to acquire excellent dynamic response and higher reliability.In accordance with the application of low output voltage, high output current, fast dynamic response requirement and so on, the half-bridge converter is proposed as the optimized topology for secondary-side control in this thesis, and the operation principle of the half-birdge converter is analyzed in detail. After that, theory design, loss analysis and efficiency estimation of the power satge are also introduced.Compared to the mature primary-side control circuit, there are new chanllenges for bias power supply, over current protecting, feed forward controlling and so on in the sendary-side control circuit. In this thesis, a kind of simple but practical bias power supply circuit is desinged, and then the PWM modulation, management function unit and the driving circuits for both primary-side and sencondary-side power MOSFETs are intorduced separately. Especially, excellent solutions for output inductor current sesensing and input voltage feed forward controlling are proposed. In the next, the closed-loop circuit is analyzed and designed through theory calculation and simulation.In the end, the experimental results of a prototype are shown to verify the design of the secondary-side control based converter with low voltage/high current output. |
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